Improvement of oxide thickness determination on MOS structures using capacitance-voltage measurements at high frequencies

It is well known that capacitance-voltage (C-V) measurements provide a simp le determination of oxide thickness, but with the scaling down of component s the classical method is not appropriated any more. We have observed that for two devices with the same oxide thickness and different surfaces, the c lassical method is accurate for large area but it is not adapted for the sm all one. We present a new procedure to make an accurate electrical determin ation of the oxide thickness on metal-oxide-semiconductor (MOS) structures of low dimensions in U.L.S.I. technology. Our method does not require a mea surement in strong accumulation. It is based on C-V measurements at frequen cies higher than I MHz associated to a non-linear optimisation of the exper imental and theoretical band bending versus bias voltage curve (Psi (S) = f (V-g)), in the depletion mode. By this way, a corrective factor is estimate d with precision in order to make an accurate determination of the oxide th ickness value. We show that the frequency associated to the non-linear opti misation of Psi (S) = f(V-g) is function of the MOS device dimensions and i s increased when the surface decreases. The experimental results obtained o n low-dimension MOS structures and different oxide thickness are precise an d in total agreement with those measured by ellipsometry. By using our new procedure the accuracy of oxide thickness determination is improved. (C) 20 01 Elsevier Science Ltd. All rights reserved.